PROJECT Dovetail key puzzle
38 The Woodworker & Good Woodworking August 2019 http://www.getwoodworking.comTEASER
BRAIN
Inspired by an article in the March 1953 issue
of The Woodworker, Peter Dunsmore puts a
modern spin on this mystifying dovetail puzzle1 Accurate setting of the radius is important 2 Start by cutting the MDF roughly to shape 3 Use double-sided tape to secure to the templateCUTTING LIST
- 150 × 76 × 25mm American walnut – 1 off
- 300 × 38 × 12.5mm Canadian maple – 1 off
- 9mm MDF for templates
H
ow can you slide a dovetail key into a
slot if the key is wider in the middle?
That is the problem. At first glance
it appears to be an impossibility and
has challenged most people who see this for the
first time. The immediate reaction is to look for
a seam lengthways in the walnut but there is
no join. The answer lies in the fact that the underside of the key is cut to a definite curve to match
that shaped across the walnut. The key is then
pushed into the slot at an upwards angle so the
wider part of the key enters the slot lower down
where the opening is wider. This isn’t a new idea;
I found the inspiration to make this from a post
war copy of The Woodworker magazine that a
neighbour was going to put into the recycling bin.Fortunately I was able to save it along with some
other copies and thought the puzzle would make
an ideal birthday present for my dad.Making the templates
As you can probably appreciate, in order for this
to work the two pieces must be cut accurately
and with care. The original article uses imperial
measurements, which actually makes more
sense for this project, but I converted these to
metric. Although the original was made entirely
with hand tools, I thought it would aid accuracy if
I used a router to cut the curves. Start by cutting
three curves onto 9mm MDF using a router fitted
to a trammel bar (photo 1). Cut one to an internal
radius of 213mm, a second to an external radius
of 213mm, then cut a third curve to an internal
radius of 121mm. Use the 213mm external radius
piece to make the small elongated MDF template
that sits on top of the key. After cutting roughly
to size (photo 2), use the previously cut template
to profile the edge with a bearing-guided trimmer.
Use double-sided tape to secure in place while
you cut the edge (photo 3). Make a copy of the
213mm internal radius template and cut straight
edges so that when the two templates are butted
together, the centre elongated template is a
secure fit between the two. The result should be
three pieces of MDF that fit together accurately
(photo 4).